The manufacture of semiconductor devices involves the performance of a series of process steps using a variety of high tech production and metrology tools in a certain order and often within a certain period of time. Photolithography is an important technology in semiconductor manufacturing. The number of masks (reticles) used in photolithography corresponds to the complexity of a manufacturing process. Photolithography affects structures of semiconductor devices, such as patterns of layers and doped regions, and determines the functional effectiveness thereof. Since photolithography is complicated, photolithography tools performing the photolithography can create a bottleneck in the manufacturing process.
A mask stocker may be used to store the masks in a wafer fabrication clean room for manufacturing. The mask stocker is a self-contained, clean environment electronic closet in which masks can be stored and from which masks can be retrieved. Generally, the cost for a mask stocker is expensive, making it impractical to provide multiple mask stockers in a factory. The mask stocker is at a specific location which operators must move to get masks for operation, a time consuming and inconvenient system. Furthermore, the operators need to manually track the location of the mask in the mask stocker, which is time consuming and can introduce human error. Such a mask stocker increases lost time of tools (e.g., photolithography tools, mask repairing tools), and decreases equipment availability and throughput of the manufacturing processes.
Thus, there is a need for an improved mask storage and retrieval system.